1. Field of the Invention
This invention relates to a water based cleaning composition. More particularly, the water based cleaning composition is one suitable for use in a tape drive.
2. Description of the Related Art
Magnetic tape is used to store information for audio and/or video recording, or for data processing applications. The tape typically consists of a substrate such as polyethylene terephthalate coated with gamma iron oxide, chromium dioxide, or other magnetic particles. The magnetic particles include microscopic areas known as "domains" which have a magnetic orientation in a particular direction. Information is recorded on the tape by intentionally orienting the domains in a precise pattern. A recording code is used to determine the pattern. For example, in digital data processing consisting only of logical zeroes and logical ones, the orientation of a domain in one direction could represent a logical zero and the orientation of a domain in the opposite direction could represent a logical one. Numerous recording codes are known. Information is recalled from the tape using the same recording code as that for recording.
The orientation of domains on magnetic tape is accomplished using a read/write "head". The head includes one or more transducers arranged so as to read and write in parallel tracks on a single magnetic tape, thereby increasing the density of stored information. A transducer includes a small core gap formed by a pair of core pieces with a coil mounted on one core piece. Excitation currents provided to the coil produce magnetic field lines that diverge from the gap to penetrate the tape in proximity thereto and orient the domains. The tape is stored on one or more reels, often contained in portable cartridges or cassettes. For the reading and writing of information, the tape must be brought in close physical proximity to the head. The portion of the tape drive in which the tape extends away from the reels to achieve such proximity to the head is known as the "tape path".
A typical tape path, such as that used in the IBM 3480 Tape Drive, is shown in FIG. 1. A magnetic tape containing cartridge 11 is removably installed at one corner of a tape drive 10. The magnetic tape 15 is wound on a tape reel 12 and includes a free end portion which can be removed from cartridge 11. The free end portion of tape 15 is automatically transported to a machine reel 13. A set of electronic circuits 21 control the rotation of reels 12 and 13 via two connections 26 and 27. Two tachometer wheels 30 and 32 provide rotational speed indicating signals to electronic circuits 21 via two connections 31 and 33.
The tape path between reel 12 and reel 13 includes a controller 16, two arcuate guides 17 and 18, a magnetic transducing head 14, and a tension idler wheel 19. Controller 16 regulates tape 15 as it is transported between reel 12 and head 14. An air supply 37 exhausts air from controller 16 through a conduit 41 for providing a vacuum chamber used in connection therewith. Arcuate guides 17 and 18 are air bearing such that positive pressure is exerted by tape 15 onto the tape-facing surface of head 14 for ensuring adequate exchange of signals between the magnetic coating on tape 15 and head 14. An air supply 37 and a conduit 40 supplies air under pressure to arcuate guides 17 and 18. Electronic circuits 21 also control the operation of air supply 37 via control lines 38. Tension idler wheel 19 is supported by a tension transducer 20 for indicating the sensed tension of tape 15 as it is being transported or held to electronic circuits 21 via a connection 22. Electronic circuits 21 thus control the movement of tape 15 between reels 12 and 13. In addition, electronic circuits 21 control the transfer of information between head 14 and tape 15. A bus 25 transfers signals between head 14 and tape 15.
Contaminants are known to accumulate in tape paths and thereby degrade performance. Performance degradation occurs in a variety of ways. The presence of contaminants between the tape and the head may interfere with the ability of the head to magnetically read and write information. The contaminants may also act as an abrasive which physically degrades the surface qualities of the tape or the head during tape movement. In addition, the contaminants may act to degrade other components of the tape path, such as those required for proper tape guidance, and cause them to function improperly.
Contaminants can reach the tape path in several ways. First, contact between the tape and various guidance portions of the tape path, including the head itself, may result in abrasion of the tape. Abrasion may also result from contact between the tape and contaminants themselves. Such abrasion results in tape debris, typically organic in nature, which tends to accumulate in certain areas of the tape path. Another source of contaminants is the surrounding environment. Airborne particles such as dust may settle on various components of the tape path. Finally, although not recognized before, cleaning compositions theoretically used to remove contaminants from tape drives may themselves leave residues.
Current cleaning methodology requires the use of solvent based fluids for the wet cleaning of tape drive components. Solvent based cleaners available throughout the world are constructed from mixtures of organic solvents. Polar degreasing solvents such as alcohols are typically used, but are quite flammable. The alcohols are thus often mixed with a fluorinated solvent to reduce the flammability of the cleaner. Fluorinated solvents, also known as chlorofluorocarbons (CFCs), have been associated with the decreasing thickness of the earth's ozone layer, thereby resulting in global warming.
An example of a tape drive cleaner including the aforementioned organic solvents is that used for the entire family of tape drives marketed by IBM Corporation (IBM). The tape cleaner currently used and recommended by IBM consists of about 64.7 weight % of 1,1,2-trichloro,1,2,2-trifluoroethane, about 35 weight % of isopropyl alcohol, and about 0.3 weight of nitromethane. In recent years, such organic solvents have become increasing targets of worldwide legislative control. The use of the solvents is gradually being limited because of the health and environmental concerns associated therewith.
Water based cleaning compositions inherently eliminate the health and environmental concerns associated with the use of organic solvents. However, the efficacy of water alone as a cleaner of organic residue is quite poor. Water based cleaning compositions therefore require additives to enhance detergency and yet maintain the solubility of salts. These cleaning compositions are designed for the cleaning of smooth, hard, reflective surfaces such as glass, tile, porcelain and other ceramic materials, steel, chrome, brass and other metallic materials, and plastics. Unfortunately, none of the water based cleaning compositions is suitable for use in tape drives, as indicated in the following paragraphs.
U.S. Pat. No. 3,173,876 discloses a water based cleaning composition consisting of less than 12 weight % ethylenediamine in water. This composition is considered inadequate for contemporary use because of the toxicity of ethylenediamine. In addition, the corrosiveness of ethylenediamine makes it incompatible with a tape drive environment in which even trace amounts of corrosion could severely impact performance. The tiny dimensions of the circuitry in the head make such especially susceptible to interference from corrosion. Additional additives recommended in relatively high levels, such as sodium phosphates and sodium borates, may further contribute to the corrosiveness of the composition. These additives are non-volatile and may therefore produce residues which are contaminants.
U.S. Pat. No. 3,463,735 discloses a water based cleaning composition including a surfactant such as a polyethylene oxide ether of fatty alcohol. The composition also includes 0.5 to 5.0 weight % organic alcohol and 0.5 to 5.0 weight % glycol. These components combine to increase lubricity, thereby making the wiping motion necessary for the application and removal of the composition relatively easy. However, lubricity is achieved by a residue left behind upon drying, a source of contaminants to be avoided in the tape drive environment. Although the organic solvents are not the primary components of the cleaning composition, they are still potentially subject to legislative controls. The preferred compositions also include sulfates and/or phosphates which again may be too corrosive for use in tape drives. Thus, none of the specified compositions are suitable for use in tape drives.
U.S. Pat. No. 4,213,873 discloses a water based cleaning composition including 0.3 weight % ammonium hydroxide and about 0.1 weight % of polyethylene glycol The use of ammonium hydroxide again makes the composition too basic and corrosive for use in tape drives. Additional compositions are disclosed but include organic alcohol solvents which should be avoided, as previously stated. Some of the additional compositions also include ammonium carbonate or ammonium bicarbonate as a lubricity agent. Although the weight % of such compounds is only about 0.025 to 0.3, they are used only in combination with substantial amounts of surfactants and alcohol solvents. There is no teaching of how to successfully clean an organic contaminant without using alcohol solvents and/or other problematic additives.
As the sophistication of tape drives increases, the need to avoid the disadvantages of the aforementioned cleaning compositions will also increase. Smaller circuitry will be required as the density of information stored on magnetic tape increases. Storage tracks currently about 400 micrometers in width may be reduced an order of magnitude. The effect of contamination or corrosion is almost certain to be catastrophic at such dimensions. Residues must be reduced. Finally, static electricity must be eliminated to prevent contaminants from resettling in the tape drive as the wiper used is removed after cleaning. Prior cleaning compositions do not adequately address static. A tape drive cleaning composition resolving the aforementioned problems would almost certainly be advantageous in general purpose use as well.